The present invention relates to the field of the medical analysis of acoustic noises, on the basis of mediate auscultation. It relates more particularly to a device for analyzing acoustic noises which are generated by the respiration of patients suffering from respiratory diseases such as cystic fibrosis, asthma or the like.
One of the major symptoms of cystic fibrosis consists of an infection of the respiratory tracts. Typical bronchial noises generally reveal such infections. This is because persons suffering from this disease generate accumulations of phlegm which obstruct the respiratory tracts while producing specific noises during respiration. The acoustic frequencies of the noises generated are a function of the size of these accumulations of phlegm and, in this context, the acoustic intensities associated with these frequencies may make it possible to estimate a degree of obstruction of the respiratory tracts. One danger which this disease represents is related to the rapid, progressive change in the size of the accumulations of phlegm, possibly giving rise to a progressive and irreversible limitation of the respiratory capacity of the patient.
It is appropriate then to monitor the progressive change in the abovementioned respiratory noises.
The usual practice consists of mediate auscultation, by means of a stethoscope. The frequencies heard give an indication as to the obstruction of the respiratory tracts. However, this indication is only qualitative, or even subjective. It is often difficult to describe sounds and to communicate a diagnosis on the basis of such subjective criteria.
A spectral representation of the respiratory noises, which is quantitative and reliable, is currently desirable. The interpretation of such a representation would make it possible to determine a progressive change in the disease.
Proposals for a spectral representation of the respiratory noises, these proposals being based on processing by Fourier transform, have recently come to light. However, the audio frequencies of the respiratory noises exhibit the feature of varying as a function of time, in particular as a function of the phase of respiration. Hence the information on the frequency of the noise, which changes substantially over time, is lost by Fourier-transform processing. This is because this type of processing is most suitable for signals which are stable over time.
The present invention then aims to improve the situation.
It relates to a device for analyzing mediate-auscultation noises, in particular respiratory noises, comprising:
an input for receiving a time-domain signal representative of an acoustic noise, sampled in a multiplicity of intensities each associated with a chosen instant,
storage means including a processing module configured to work together with calculating means with a view to evaluating a set of transformed intensities, each associated with a predetermined audio frequency, while the storage means are further configured to store said transformed intensities in memory, and
an output linked, on the one hand, to the storage means in order to deliver each transformed intensity in correspondence with an associated frequency, and, on the other hand, to means for representing the transformed intensities as a function of the frequencies, with a view to obtaining a spectral representation of the auscultation noise.
According to a general characteristic of the invention, the processing module is configured to evaluate a set of transformed intensities for each chosen instant, while the storage means are configured to store in memory each transformed intensity as a function of an associated frequency, on the one hand, and of a chosen instant, on the other hand, which makes it possible to obtain a three-dimensional representation of the auscultation noise in terms of time and of frequency.
According to a second important characteristic of the invention, the processing module is configured to evaluate the set of transformed intensities for each chosen instant, by producing, for each frequency, a sum over a multiplicity of current instants of terms resulting from a product involving, for each current instant, the intensity associated with the sum of the chosen instant and of the current instant, on the one hand, and the complex exponential of a pure imaginary product of the frequency and the current instant, on the other hand.
According to a third important characteristic of the invention, the processing module is further configured to evaluate a phase for each intensity, as a function of a difference between the associated chosen instant and a chosen start instant, with a view to attributing, to each intensity, a complex value and its conjugate value, while the terms of said sum are representative of products involving, for each current instant:
a) the complex intensity associated with the sum of the chosen instant and of the current instant,
b) the conjugate complex intensity, associated with the difference in the chosen instant and in the current instant, and
c) said complex exponential which makes it possible to obtain a spectral representation of the auscultation noise, while preserving a real-time scale.
According to one advantageous characteristic of the invention, the storage means further comprise chosen coefficients, for weighting of the terms of said sum, each associated with a current instant.
Advantageously, the The device as claimed in the invention includes visual-display means of the type comprising a monitor and/or a printer, while the representation means includes a graphics-representation module, able to work together with the visual-display means in order to represent the transformed intensities graphically, as a function of the associated frequencies, on the one hand, and of the chosen instants, on the other hand, forming three-dimensional spectra in terms of time and of frequencies.